I. Field of the Invention
This invention relates to ambulatory devices for physically handicapped individuals and, in particular, to an ambulatory wheelstand having multiple angular positions in which the center of gravity of the user remains centrally disposed above a particular location on the wheelstand frame.
II. Description of the Prior Art
Ambulatory devices have been used to enable a non-ambulatory person, such as a paraplegic or a quadraplegic, to move about more or less on his own. Typical wheelchairs were the first types of ambulatory devices, but required the user to remain in one position, thus causing atrophy of the muscles.
Wheelstands first resembled a cross between a wheelchair and a gurney and employed a foldable or a pivotable stretcher portion which could pivot between a horizontal and an upright position. Examples of these earlier wheelstands can be found in U.S. Pat. Nos. 2,295,006 to Philips and 2,986,200 to Nobile. Each of these patents discloses a device having a large central driving wheel rotatably attached to a frame stabilized by castor wheels at the front and the rear of the device. The patient support is pivotably secured to the frame and includes either a straight stretcher or a somewhat chair-shaped platform to support the user. The support is pivotable between an upright position and a horizontal position. Because of the relatively high pivoting point of the support structure of these devices, the center of gravity of the devices is quite high, rendering the device somewhat unstable. The front and rear castor wheels are required to improve stability.
An improved ambulatory wheelstand is disclosed in U.S. Pat. No. 4,620,714 to Davis.
U.S. Pat. No. 4,310,167 to McLaurin disclosed what the inventor calls a center of gravity wheelchair with an articulated chassis. This wheelchair also has a large drive wheel centrally located and both front and rear castor wheels. The chassis is articulated so that the user can shift the center of gravity of the device forward by operation of a lever which extends the chassis frame and the front castor wheel, thus elongating the frame and improving the stability. This device is particularly useful for negotiating curbs, hills or the like. However, McLaurin still employs front and rear castors and requires the user to assume a sitting position only.